Low pressures affect the balance of the vehicle:
- A reduction in pressure on the front axle will tend to increase the chances of understeer (car turns less than you would expect).
- A reduction in pressure on the rear axle with tend to increase the chances of oversteer (car turns more than you would expect).
Low pressures and the effect on tyre life:
A tyre that is under inflated by 20% will have a reduction in life of just over 20%
Low pressure and the effect on your fuel consumption:
A set of under inflated tyres will have the effect of causing the engine to work harder (and this will increase your fuel consumption or decrease your fuel efficiency).
Remember the objective is to maximize tire grip and the beauty is that maximum grip means even temperatures across the tire.
In any case, I believe that tire pressure has been generally overlooked since most people are not sure how it affects the cars in F1CE, but I also belive that there is lots to win by experimenting with it.